Modulating circuit



July 28, 1942. w. HAGEN MODULATINQGIRCUIT Filed May 12, 1939 FigaPatented July 28.19.42 n

Wolfgang Hagen,

Berlin, Germany, assignor to C. Lorenz Aktiengesellschaft,Berlin-Tempelhof, Germany, a company.

. v Application May 12, 1939, serial No. 273,313

In Germany May 14, 1938' 2 Claims. 'l (Cl. 179-1715) The modulatingcircuits employed in carrier frequency systems must have a coefficientof non-linear distortion which with a high degree of modulation shouldbe as small as possible. This requirement arises especially in the case,of the so'ca1led line radio, that is, systems in which speech, music,and the like is transmitted over telephone lines. The modulatingcircuits used in systems of this kind are in the nature of a bridgeconnection comprising rectiers or amplifying tubes and have acurrent-voltage-` The arrangement shown in Fig. 2, is a bridge typemodulating circuit fitted with amplifying tubes. Also here the frequencyvfl is conveyed over transformer UI to a bridge B While thecharacteristic which with small values greatly diers from the idealcharacteristic necessary for obtaining a small coeflici'ent ofnon-linear distortion. Therefore in such circuits the rectication in thecase of high degrees of modulation, that is to say, in the case of highvoltage amplitudes, will fail to be linear, thus producing distortion.

The present invention proposes to provide modulating circuits of thiskind with a counter coupling adapted to'render the modulationcharacteristic linear.

In the accompanying drawing two embodiments of the invention areillustrated.v

Fig. 1 shows the circuit arrangement of one embodiment, while Fig. 2 isa diagrammatic representation of the other.

The modulator here shown comprises an input transformer UI over whichthe carrier frequency fl arrives, and also comprises rectiers GI, G2,such for instance as diodes or dry rectiflers, and an output transformerU2.. The second or modulating frequency f2 is conducted to the points A.The product of ymodulation of this lbridge arrangement 'is amplified byan electron tube R` and leavesv the modulating arrangement over anoutput transformer U3.

Part of the output amplitude is conveyed through a phase' and amplitudecorrecting device X to the transformer UI. The construction elements ofthe modulator are so calculated that the voltage returned by device X isin phase opposition `with respect tothe input voltage. By

this means a counter coupling is produced that acts to decreasenon-linear effects arising in the' modulator.

by way of example frequency f2 is conveyed to this bridge over atransformer U. In the arms of bridge B am- 4 plifying tubes RI, R2, suchas triodes, for example, are -included as non-linear members. On l theoutput side the product of modulation is' derived over transformer U2.The counter coupling is effected by the intermediary of phase andamplitude correcting devices YI, Y2 by which the two sides of the outputtransformer are connected with the appertaining sides of the inputtransformer. An arrangement of this kind will not affect the. symmetryof the modulating circuit and also allows of adjusting the properties ofthesaid correcting devices independently of each other.

Equally, the modulation may be effected by lmeans of an electron tubearranged to cooperatewith an appropriate counter coupling.

What is claimed is:

1. A modulation arrangement comprising abalanced plurality' of rectifierelements, a carrier input channel including a transformer, a signalinput channel, an amplifier having an input and an output; means .forapplying carrier Waves from,

said carrier input' channel and signal waves from said signal inputchannel to said rectifier elements for modulating said carrier Waves bysaid signal waves, connections fordelivering from ,said elements to theinput of said amplier only carrier waves and modulation products, saidconnections being symmetrically arranged with respect to said signalwaves so as to balance these out, and feedback means for feeding backcarrier waves from the output-of said amplifier to lreduced.

the primary side o f said transformer in phase opposition to the wavessupplied thereto froml said carrier input channel whereby distortion is2. An arrangement according to claim 1 b wherein said amplier is ofunbalanced type and s wherein said feedback means comprises unbalancedconnections for effecting said feedback of carrier waves to saidprimary. A. l .WOLFGANG HAGEN.

